A gas water heater typically endeavors to supply hot water with a constant temperature. Some influences that impact the temperature of the hot water from traditional gas water heaters include: gas quantity, water flow, and air delivery. During the control of the temperature of the water supply, due to the consideration of safety and environmental protection, the water heater balances the gas quantity and the air delivery (e.g., controlled by a fan) to ensure the complete combustion of the gas. The control of the water temperature becomes a complicated operation that needs to take into integral consideration of multiple factors. As a result, the control may attend to one factor and lose another; therefore, it cannot reach a perfect control effect. In addition, a gas water heater can include the followings concerns.
1. In order to promote safety, when the gas water heater starts, the fan should operate prior to ignition. When the gas water heater stops, the fan should stop after the flameout. Therefore, for frequent use of small amounts of water, a long time to wait for a rising temperature may occur. This wastes water and gas, as well as makes people feel uncomfortable.2. Upon each start, the gas water heater makes a noise of the fan purging and ignition, which can disturb people.3. The control actuator (such as a proportional valve) is complicated in its structure, and also needs the help of mechanical action. Therefore, during the action of the actuator, there can be an “overshoot”, i.e. the temperature of the water is offset from the control value in transient time. This can make people using the water uncomfortable.
The public specification of Chinese patent application number 02226554.6 provides an adjustable constant temperature gas water heater. This heater is characterized in that: a solenoid valve for each gas nozzle of the main burner and several water temperature controllers of different temperature on the hot water pipe. The user can set the water temperature by the temperature regulator, which controls the opening of solenoid valves in order to obtain water with constant temperature. This technique is not only complicated in temperature control, but the constant temperature control is a step-type. Therefore, the temperature control may not provide accurate control and cannot overcome the above-mentioned defects.
The public specification of Chinese patent application number 200620058136.9 provides a central water heater. The central water heater is characterized in that: electric storage water heater and gas water heater are connected in series. Therefore, the heater has the advantages of both electric storage water heater and gas water heater, not only for fast hot water supply, but also for continuous hot water supply. However, this heater does not concern a constant temperature control.
The public specification of Chinese patent application number 01206912.4 provides a constant temperature gas instant water heater, for which, the electric heating water storage thermostat is installed on one side of constant temperature gas water heater and the water storage tank of the electric heating water storage thermostat is equipped with a multi-hole water inlet pipe. The pipe is connected to the water outlet pipe of the gas heat exchanger by a connector. The connector is installed with a temperature sensor that is connected to an intelligent controller via a conductor. According to the description, there is hot water supply once the water heater is opened, there is cooler water during intermittent use, and the temperature of water keeps constant. But theoretic analysis and practice show the following shortages: 1. the multi-hole water inlet pipe of the electric water heater is complicated in its structure; 2. the electric heating portion adopts water storage type, so that it will still need a certain time to heat the water in practice; 3. the electric heating device works by a switching method; therefore, it has thermal inertia and cannot keep a constant temperature for the water; 4. the water temperature sensor is installed at the water inlet of electric water heater, which can not acquire an accurate temperature at the water outlet and influences the control on water temperature.